Wave front synthesis technique is known as a sound field reproduction method to acquire a wave front of sound in a sound field by a plurality of microphones and to reproduce the sound field on the basis of the acquired sound signal. As one type of the wave front synthesis technique, there is a boundary surface control method (for example, see Patent Document 1).
The boundary surface control method is a method to arrange microphones in a reproduction space where the sound field is reproduced in the same manner as that in the original space where a sound source has been acquired and to provide input signals to a plurality of speakers installed in the periphery of the reproduction space such that signals observed by the microphones are the same as microphone signals acquired in the original space.
In this boundary surface control method, a speaker that outputs a spherical wave in every frequency band is ideal as the plurality of speakers installed in the periphery of the reproduction space; however, no such speaker exists in reality.
Therefore, generally used is a multi-way speaker where a plurality of units is included in one enclosure to support by dividing into a plurality of bands such as a high frequency band side and a low frequency band side.